1. Field of the Invention
The present invention relates to a method for forming conductive patterns. More specifically, the present invention relates to a method for forming conductive patterns, which is capable of preventing a substrate from being deformed during firing of conductive patterns and enabling a firing process to be easily performed.
2. Description of the Related Art
Conductive patterns are necessarily formed in transparent substrates for displays or circuit boards for electronic parts which are recently used.
Such conductive patterns are often formed by a photosensitive paste method, or a photo-etching method. In the photosensitive paste method, a photosensitive electrode paste is applied on a substrate using a screen printer. Then, the substrate is exposed to UV using a photomask. A portion of the photosensitive electrode paste which is exposed to UV is photo-crosslinked and thus not etched by an aqueous alkaline solution. On the contrary, another portion of the photosensitive electrode paste which is not exposed to UV is not photo-crosslinked and thus etched by an aqueous alkaline solution. Consequently, an electrode pattern is formed on the substrate. However, such a method of forming an electrode using a photosensitive electrode paste has a disadvantage that it is difficult to control the pitch accuracy and the electrode width.
Meanwhile, in the photo etching method, an electrode is mainly formed by an entire-surface coating or a vapor deposition/etching process. However, such a method of forming an electrode by vapor deposition has problems of prolonged process time, high cost of a thin film-forming device and material, and environmental pollution due to etching. Therefore, an attempt to replace conventional processes by printing methods such as inkjet, offset and gravure printings has been recently proposed.
Using such printing methods, the unnecessary consumption of material may be reduced by printing only a required amount of material on necessary regions, and the process may be simplified as it is unnecessary to use a mask.
Forming of patterns by printing involves a firing process, and residual organic substances and solvents must be removed by the firing process to impart conductivity to a metal. As a firing process, various firing processes ranging from firing by a traditional electric furnace to firing by recent microwave or plasma firing are applied. Particularly, the microwave firing is remarkable in that it is able to fire selectively by increasing only the temperature of metal wiring absorbing microwave without thermal-impact on a substrate, thereby obtaining a product having the same quality as that obtained from a high-temperature firing in short time and also preventing the substrate from being damaged.
However, in case of the microwave firing, thermal energy is only concentrated on wiring, and therefore, a difference in shrinkage between the wiring and substrate may be greater than that in the case of other firing methods, thereby leading to the deformation of the substrate. Particularly, such deformation may occur more severely in a flexible substrate such as PET which is popularly used in recent years.